1. Field of the Invention
The present invention relates to a rechargeable battery utilizing intercalating and deintercalating reactions of lithium ions as charging and discharging reactions of the battery, and particularly to a rechargeable lithium battery having a large electric capacity, which employs a carbonous material as an anode.
2. Related Background Art
In recent years, the warming of the earth because of the so-called greenhouse effect due to an increase of atmospheric CO.sub.2 has been predicted. For example, in thermal electric power plants, thermal energies obtained by burning a fossil fuel such as coal or petroleum are being converted into electric energies, and along with burning such a fuel, a large amount of CO.sub.2 gas is being exhausted in the air; accordingly, in order to suppress the above earth-warming phenomenon, there is a tendency to prohibit the establishment of new thermal electric power plants. Under such circumstances, so-called load leveling practice has been proposed in order to effectively utilize the electric power generated by power generators in thermal electric power plants or the like. According to this practice, surplus power unused in the night is stored in rechargeable batteries installed at general houses and the power thus stored is used in the daytime when the demand for power increases, whereby the power consumption is leveled.
In the application of electric vehicles which do not exhaust any air polluting substances including COx, NOx and CH, there is an increased demand for developing a high performance rechargeable battery with a high energy density. Also, in the application of portable instruments such as small personal computers, word processors, video cameras, and pocket telephones, there is an increased demand for developing a miniature, lightweight, and high performance rechargeable battery.
As for the above miniature, lightweight and high performance rechargeable battery, one example using a lithium-graphite intercalation compound as an anode of a rechargeable battery has been reported in JOURNAL OF THE ELECTROCHEMICAL SOCIETY 117, 222 (1970), and since then, various rocking chair type rechargeable batteries, so-called "lithium ion batteries" have been developed and practically used in part, in which a carbonous material is used as an anode material and an intercalation compound introduced with lithium ions is used as a cathode material wherein lithium ions are stored in a state being intercalated between layers of the carbonous material upon conducting the charging reaction of the battery. More specifically, in such a lithium ion battery, a carbonous material functioning as a host material for allowing lithium ions to intercalate between layers thereof as a host is used as an anode, to suppress the dendrite growth of lithium upon conducting the charging of the battery, thereby prolonging the cycle life of the charging and discharging cycle.
In order to further prolong the cycle life of rechargeable batteries of this type, proposals and studies have been extensively made to further improve carbonous materials used for anodes of the batteries. In general, carbonous materials usable for the above anodes, which are capable of storing lithium upon conducting the charging, are classified into difficult-to-graphitize carbonous materials (i.e., materials obtained by sintering and carbonizing a resin which contains many amorphous components and is easily graphitized) and graphite series materials.
Japanese Unexamined Patent Publication No. 122066/1987 discloses a rechargeable battery using, as an anode of a type utilizing intercalating/deintercalating phenomenon of ions of an alkali metal, a carbonous material having an atomic ratio of hydrogen/carbon in a range of less than 0.15, a spacing between the (002) faces in a range of 0.337 nm (nanometer) or more, and a magnitude of a crystallite along the c-axis in a range of 15 nm or less.
Japanese Unexamined Patent Publication Nos. 66856/1990 and 252053/1991 disclose a rechargeable battery (nonaqueous electrolyte solution type rechargeable battery such as lithium battery) using, as an anode, a carbonous material having a spacing between the (002) faces in a range of 0.370 nm or more, a true density in a range of less than 1.70 g/cm.sup.3, and a specific property having no heat generation peak at a temperature of 700.degree. C. or more as a result of a differential thermal analysis conducted in an air flow.
Japanese Unexamined Patent Publication No. 245473/1991 discloses a rechargeable battery (nonagueous electrolyte solution type rechargeable battery such as a lithium battery) using, as an anode, a carbonous material having a spacing between the (002) faces in a range of from 0.33 nm to 0.35 nm, a magnitude of a crystallite along the c-axis in a range of from 5 nm to 20 nm, and a magnitude of a crystallite along the a-axis in a range of from 10 nm to 40 nm.
Japanese Unexamined Patent Publication No. 290844/1993 discloses a rechargeable battery using, as an anode, a mixture of natural graphite and synthetic graphite, and Japanese Unexamined Patent Publication Nd. 84516/1994 discloses a rechargeable battery using, as an node, graphite having the surface covered with an amorphous carbon layer or a coke layer.
Other than the above examples, there have been reported various kinds of carbonous materials applied to anodes of batteries: for example, carbon fibers Denki Kagaku (Electrochemistry), Vol. 57, p614 (1989)!; mesocarbon microbeads Abstract of the 34th Symposium on Battery (in Japan), p77 (1993)!; natural graphite Abstract of the 33rd Symposium on Battery (in Japan), p217 (1992)!; graphite whiskers Abstract of the 34th Symposium on Battery (in Japan), p77 (1993)!; and sintered body of furfuryl alcohol resin Abstract of the 58th Annual Meeting of Electrochemistry of Society, p158 (1991)!.
However, as for the above difficult-to-graphitize carbon series material, particularly, used as an anode of a rechargeable battery utilizing intercalating and deintercalating reactions of lithium ions as the charging and discharging reactions, although there has been developed a carbonous material exhibiting an electric capacity over a theoretical capacity of graphite (372 mAh per 1 g of carbon, this theoretical capacity meaning the fact that one lithium atom is stored per six carbon atoms) at the beginning of the charging, the carbonous material has a problem that the electric capacity has a value lower than the theoretical capacity after the repetition of the charging and discharging cycle by several tens or several hundreds times. On the other hand, as for the above graphite series carbonous material, particularly, used as an anode of a rechargeable battery using intercalating and deintercalating reactions of lithium ions as the charging and discharging reactions, there has not been developed a carbonous material exhibiting an electric capacity over the theoretical capacity of graphite. Accordingly, there is a strong demand for developing a lithium battery using a carbonous material as an anode, which can be increased in electric capacity and improved in cycle life.